The prior art is replete with various configurations of nonvolatile random access magnetic memory structures. For example, U.S. Pat. No. 4,791,604 describes one such structure comprising a substrate including a plurality of ferromagnetic domains disposed at a corresponding plurality of distinguishable locations, or cells, generally arranged in a matrix of word rows and bit columns.
The structure of U.S. Pat. No. 4,791,604 includes fixed drive means for selectively generating magnetic fields at selected locations to write bits into the domains thereat (i.e. establish the ferromagnetic state of the domain) comprising either a logical 1 or 0. The fixed drive means generally comprises a plurality of word drive lines, i.e. one for each word row, and a plurality of bit drive lines, i.e. one for each bit in a word. In order to write a bit into a particular domain, half magnitude select currents are driven through both the word drive and bit drive lines associated with that domain. The domain will switch states only if the magnetic fields produced by the respective drive currents are additive, i.e. act in the same direction.
The structure of U.S. Pat. No. 4,791,604 also includes fixed sensing means for sensing the respective magnetic states of said domains. In various embodiments described in said U.S. Pat. No. 4,791,604, the fixed sensing means comprise either a conductive line, a Hall effect device or a semiconductor thyristor disposed in proximity to the domain.
Other exemplary U.S. Patents relating to nonvolatile random access memories, and drives and sense means therefor, include 3,370,185; 3,651,311; 3,701,126; 3,714,559; 3,825,777; 3,852,725; 3,829,883; 4,027,300; 4,048,648; 4,129,880; 4,163,986; 4,250,518; 4,276,555; 4,288,708; 4,516,144; 4,677,380; 4,689,648; and 4,698,522.